On Parallel and Concurrent Security of HB and HB

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On Parallel and Concurrent Security of HB and HB
Jonathan Katz and Ji-Sun Shin University of
Maryland
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Motivation

• Juels and Weis analyze and propose the HB and HB
  protocols (tomorrow)
• Building on prior work of Hopper-Blum
• HB secure against passive adversaryHB secure
  against active adversary
• They are extremely efficient
• Suitable for low-power devices

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But

• Juels-Weis analyze basic, two-round protocols
  with soundness ½
• Then claim security under sequential repetition
• Yields protocols with O(k) rounds!
• Also, no security under concurrent executions

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Our Results

• Using recent results of Regev (STOC 05), we
  prove security of HB/HB under concurrent
  executions
• HB/HB can be collapsed to only 2-3 rounds!
• We believe our approach also greatly simplifies
  the proofs